Calcium inhibits urinary acidification: effect of the ionophore A23187 on the turtle bladder

The role of intracellular calcium in urinary acidification was studied in the turtle bladder with the use of the ionophore A23187. In the presence of calcium acidification was significantly inhibited in the hemibladders treated with the ionophore as compared to control hemibladders treated with dimethylsulfoxide (the vehicle used to dissolve the ionophore). In the absence of calcium both the ionophore and dimethylsulfoxide failed to cause any change in acidification. The apparent proton motive force and active conductance of H+ were unchanged in dimethylsulfoxide treated hemibladders. In the presence of the ionophore and calcium, the proton motive force and the conductance were significantly decreased when the H+ current was low (less than 30% of control values); when the H+ current was decreased, but not less than 30%, the proton motive force was unchanged. These data provide evidence for an important role of intracellular calcium in the regulation of urinary acidification.